Effect of adsorbed fibronectin concentration on cell adhesion and deformation under shear on hydrophobic surfaces

To facilitate tissue integration with biomaterials proteins and peptides frequently are immobilized on the biomaterial surface. In particular, extracellular matrix proteins--which interact specifically with integrin adhesion receptors on the cell surface--can stimulate initial cell attachment by serving both as a ligand for receptor-mediated attachment and as a stimulant of focal adhesion formation and cytoskeletal reorganization. Consequently, the strength of cell adhesion should depend both on the strength of cell/surface contacts and cytoskeleton-dependent properties of the cell (i.e., morphology, compliance). To examine this dual role of extracellular matrix proteins, murine fibroblasts were seeded onto self-assembled monolayers (SAMs) of dodecanethiolate coated with 0 to 0.45 microg/cm(2) of fibronectin (Fn) and then detached by hydrodynamic shear using a radial-flow chamber (RFC). Cell adhesion was characterized in terms of the critical wall shear stress for detachment (tau(wc)), and the compliance was evaluated from measurements of cell displacement and elongation as a function of the fibronectin concentration. Critical wall shear stress and cell displacement were found to be insensitive to Fn at concentrations below 0.23 microg/cm(2) while above this threshold tau(wc) increased and displacement decreased with increasing Fn concentration. Elongation of the cells in the direction of flow was independent of Fn concentration, but correlated linearly with tau(wc) for Fn densities below 0.23 microg/cm(2). These studies show that Fn concentration affects both tau(wc) and cell displacement under shear, and that tau(wc) is sensitive to cell compliance. In addition, they suggest that the dominant mechanism of cell detachment from hydrophobic substrates involves cell displacement.